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  • 1
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    Methods for local gravity field approximation (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The most widely known modern method for estimating gravity field values from observed data is least-squares collocation. Its advantages are that it can make estimates at arbitrary locations based on irregularly spaced observations, and that it makes use of statistical information about errors in the input data while providing corresponding information about the quality of the output estimates. Disadvantages of collocation include the necessity of inverting square matrices of dimension equal to the number of data values and the need to assume covariance models for the gravity field and the data errors. Fourier methods are an important alternative to collocation; having the advantage of greater computational efficiency, but requiring data estimates to be on a regular grid and not using or providing statistical accuracy information. The GEOFAST algorithm is an implementation of collocation that achieves high computational efficiency by transforming the estimation equations into the frequency domain where an accurate approximation may be made to reduce the workload. The forward and inverse Fast Fourier Transforms (FFTs) are utilized. The accuracy and computational efficiency of the GEOFAST algorithm is demonstrated using two sets of synthetic gravity data: marine gravity for an ocean trench region including wavelengths longer than 200 km; and local land gravity containing wavelengths as short as 5 km. These results are discussed along with issues such as the advantages of first removing reference field models before carrying out the estimation algorithm.
    Keywords: GEOPHYSICS
    Type: Ohio State Univ., Progress in the Determination of the Earth's Gravity Field; p 77-80
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  • 2
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    Terrestrial impact melts as analogues for the hematization of Martian surface materials (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Visible and near-IR reflectivity and Mossbauer data were obtained on powders of hydrothermally-altered impact melt sheets from West Clearwater Lake, Manicouagan, and Ries (Polsingen) impact structures. The data support previous interpretations that Martian bright regions spectra can be interpreted by a ferric-bearing phase that has a relatively featureless absorption edge together with some well-crystalline (bulk) hematite to account for the 860 nm hematite band. The data also show that bands at wavelengths longer than 900 nm, which are characteristic of Martian dark regions, occur when both hematite and pyroxene are present. It thus follows that hematization of Mars can be attributed, at least in part, to hydrothermal alterations of impact melt sheets. Impact heating could also form bulk-Hm from nanophase ferric oxides.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., Twenty-Fourth Lunar and Planetary Science Conference. Part 2: G-M; p 1015-1016
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  • 3
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    Combined Backscatter Moessbauer Spectrometer and X Ray Fluorescence analyzer (BaMS/XRF) for planetary surface materials (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: A backscatter Moessbauer spectrometer (BaMS) with included x ray fluorescence (XRF) capability for the Mars Environment Survey (MESUR) Mission, which has been proposed by NASA for 1998, is being developed. The instrument will also be suitable for other planetary missions such as those to the Moon, asteroids, and other solid solar-system objects. The BaMS would be unique for MESUR in providing information about iron mineralogy in rocks, clays, and other surface materials, including relative proportions of iron-bearing minerals. It requires no sample preparation and can identify all the normal oxidation states of iron (3+, 2+, 0). Thus, BaMS is diagnostic for weathering and other soil-forming processes. Backscatter design allows the addition of XRF elemental analysis with little or no modification. The BaMS/XRF instrument complements the thermal analyzer with evolved gas analyzer (TA-EGA) and the alpha-proton x-ray spectrometer (APXS) proposed (along with BaMS) for geochemical analysis on MESUR.
    Keywords: GEOPHYSICS
    Type: Program and Abstracts for Clay Minerals Society 28th Annual Meeting; p 1
    Format: text
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  • 4
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    UV, visible, and near-IR reflectivity data for magnetic soils/rocks from Brazil (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The objective is to obtain UV, visible, and near-IR reflectivity spectra for several magnetic Brazilian soils/rocks and compare them to corresponding data for Mars to see if these materials satisfy both magnetic and spectral constraints for Mars. Selected physical properties of the magnetic Brazilian soils/rocks are presented. In general, the spectral features resulting from ferric crystal-field transitions are much better defined in the spectra of the magnetic Brazilian soils/rocks than in Martian spectral data. Presumably, this results from a relatively higher proportion of crystalline ferric oxides for the former. The apparent masking of the spectral signature of maghemite by hematite or goethite for the Brazilian samples implies the magnetic and spectral constraints for Mars can be decoupled. That is, maghemite may be present in magnetically-significant but optically-insignificant amounts compared to crystalline hematite.
    Keywords: GEOPHYSICS
    Type: Program and Abstracts for Clay Minerals Society 28th Annual Meeting; p 161
    Format: text
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  • 5
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    Measurements of the total electron content and the equivalent slab thickness of the midlatitude ionosphere. (1965)
    In:  Other Sources
    Details
    Publication Date: 2019-05-24
    Description: Total electron content and equivalent slab thickness of midlatitude ionosphere determined from radio transmissions of Transit IVA Earth satellite
    Keywords: GEOPHYSICS
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  • 6
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    Measurements of the Total Electron Content and the Equivalent Slab Thickness of the Mid-latitude Ionosphere (1964)
    In:  CASI
    Details
    Publication Date: 2019-05-29
    Description: Transit IVA satellite and ionosonde differential Doppler data for mid-latitude ionosphere total electron content and equivalent slab thickness
    Keywords: GEOPHYSICS
    Type: NASA-CR-60710
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  • 7
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    Diurnal variation of large-scale ionospheric irregularities. (1966)
    In:  Other Sources
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    Publication Date: 2019-05-30
    Description: Diurnal variation of ionospheric irregularities, using differential Doppler method for analysis of data transmitted by Beacon satellite
    Keywords: GEOPHYSICS
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  • 8
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    Variation of electron spectrum and intensity at low altitudes. (1965)
    In:  Other Sources
    Details
    Publication Date: 2019-05-24
    Description: Variation of electron spectrum and intensity at low altitudes measured by polar orbiting satellites in 1962 and 1963
    Keywords: GEOPHYSICS
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  • 9
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    Atmospheric lidar multi-user instrument system definition study (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A spaceborne lidar system for atmospheric studies was defined. The primary input was the Science Objectives Experiment Description and Evolutionary Flow Document. The first task of the study was to perform an experiment evolutionary analysis of the SEED. The second task was the system definition effort of the instrument system. The third task was the generation of a program plan for the hardware phase. The fourth task was the supporting studies which included a Shuttle deficiency analysis, a preliminary safety hazard analysis, the identification of long lead items, and development studies required. As a result of the study an evolutionary Lidar Multi-User Instrument System (MUIS) was defined. The MUIS occupies a full Spacelab pallet and has a weight of 1300 kg. The Lidar MUIS laser provides a 2 joule frequency doubled Nd:YAG laser that can also pump a tuneable dye laser wide frequency range and bandwidth. The MUIS includes a 1.25 meter diameter aperture Cassegrain receiver, with a moveable secondary mirror to provide precise alignment with the laser. The receiver can transmit the return signal to three single and multiple photomultiple tube detectors by use of a rotating fold mirror. It is concluded that the Lidar MUIS proceed to program implementation.
    Keywords: GEOPHYSICS
    Type: NASA-CR-3303
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  • 10
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    Spatial resolution and repeatability of Magsat crustal anomaly data over the Indian Ocean (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Preliminary results from analysis of individual Magsat tracks in the eastern Indian Ocean demonstrate the resolution capability and repeatability of these data. Spectrum analysis indicates that 250 km is the absolute lower limit for resolving crustal magnetic anomalies in Magsat along-track data. Spectral coherence analysis of closely-spaced tracks shows that magnetic anomaly features with wavelengths greater than 700 km are highly repeatable from track to track.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 9; Apr. 198
    Format: text
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